The invention relates in general to planar monopole antennas and in particular to planar monopole antennas with sleeve structures.
Embedded antennas, such as chip antennas and planar antennas, are widely applied in wireless communication devices. A conventional type is a ceramic chip antenna produced by LTCC (Low Temperature Co-fired Ceramic) technology. Conventional planar antennas such as microstrip antennas, printed antennas and Planar Inverted F Antennas (PIFAs), are generally applied in GSM, DCS, UMTS, WLAN, and bluetooth wireless equipment such as mobile phones and wireless LAN adapters.
Referring to FIG. 1, a conventional planar monopole antenna primarily comprises a substrate S, a ground G, a radiator R and a cable W. The ground G and the radiator R are formed on a surface S1 of the substrate S, and the radiator R is longitudinal along axis Y.
The cable W, such as a coaxial cable, comprising a signal wire W1 and a ground wire W2 enclosing the signal wire W1. As shown in FIG. 1, the radiator R comprises a feed end RF adjacent to the ground G. The feed end RF is connected to the signal wire W1, and the ground G is connected to the ground wire W2, respectively.
With respect to typical frequency range of Digital Video Broadcasting (460˜860 MHz), the frequency coverage ratio of a conventional planar monopole antenna as shown in FIG. 1 is usually less than 30%, adversely affecting communication efficiency.